good evening, david. >> reporter: diane, good evening. we are coming to you live from tehran tonight. iran has allowed us in at this critical moment. the u.s. and much of the west convinced that iran continues to work toward those nuclear weapons. iran, of course, denying this and, as you point out, we are just days away now from the u.s. and iran joining a small group of others as they return to the negotiating table. we landed in iran, in a country where american journalists are rarely allowed to visit. and rarer still, we were given access to the people, the streets of tehran. above ground, a bustling city of 12 million. below ground, we discover a gleaming subway system, far quieter and cleaner than the famous subways of new york city. and there was something else very different. this says "women only" right here. the back of the train, reserved for women. but beyond the trains, the traffic, everywhere you look, there is something else on the move here. the prices. skyrocketing inflation. their currency losing 80% of its value in just